This application claims the benefit of co-pending German Patent Application No. 199 20 07-1,8 entitled xe2x80x9cVorrichtung zum xc3x9cberziehen von Warenstxc3xccken, insbesondere Sxc3xcxcex2warenstxc3xccken, mit einer fliexcex2fxc3xa4higen xc3x9cberzugsmassexe2x80x9d, filed on May 3, 1999.
The present invention generally relates to an apparatus for coating articles with a liquid coating material. More particularly, the present invention relates to an apparatus for coating candy bars with tempered chocolate mass as liquid coating material.
Apparatuses for coating articles with liquid coating material are commonly known in the art. Apparatuses of this kind are also called coaters. They are used in the production lines of chocolate candy, chocolate bars, fine cakes and pastries and the like to form a coating or a cover over the articles. Often tempered chocolate mass is used as coating material. However, other coating material can be used, for example fats or sugar masses.
An apparatus for coating articles with liquid coating material is known from U.S. Pat. No. 5,954.876. The apparatus includes an endless conveyor belt for transporting the articles to be coated from the entrance toward the exit through said apparatus. The articles lie on said conveyer belt while being coated with the liquid coating material. There are means for coating the articles mounted at least one above the conveyor belt. The liquid of flowable mass is circulated in surplus in the apparatus and falls down in a curtain-like shape in a free downwardly directed descent. A substructure of the apparatus has a housing-like tub including a run-off plate at the bottom to catch the excess coating material being pumped again upwardly for recirculation. The run-off plate is located below said endless conveyer belt and is part of the tub to collect the excess coating material. A scraping belt is arranged below the conveyor belt and above the run-off plate for moving the excess coating material and for scraping the coating material from the run-off plate, wherein the scraping belt includes a plurality of transverse struts. The transverse struts travel immediately above the run-off plate, are rotatably mounted in chains, and can have a circular cross section. The transverse struts always have contact to the surface of the run-off plate to be able to scrap the excess coating material from the run-off plate. The scraping belt is driven continuously. Due to the contact of the scraping belt with the surface of the run-off plate a heat flux at this place cannot be hindered. It is common practice to design the housing-like tub in a double-walled manner and to connect the spacing between the two walls, i.e. the spacing between the outer wall of the tub and the run-off plate, with a protection heating often in form of a circuit of warmed circulating water.
The warmed circulating water has to have a higher temperature than the tempered coating material on the run-off plate to prevent a subcooling and a detempering of the coating material. In case of subcooling there is the danger that the coating material unfortunately gets in solid condition on the run-off plate. On the other hand, especially when coating is effected using chocolate masses, it is important to avoid a heating up to higher temperatures with subsequent detempering. It is not possible to use detempered chocolate masses to coat articles with a good quality of the coating. Using a scraping belt as a unit assisting the recirculation of the surplus coating material on said run-off plate means to have a substantial heat flux into the coating material. On the other hand, the cross section of the struts is smaller than the thickness of the layer of the coating material on the run-off plate. Thus, only part of this layer is contacted by the struts and this makes it necessary to drive the unit containing the struts continuously. This continuous motion mixes a lot of air into the circulating coating material which often is a disadvantage.
The used coating materials of different kind, like chocolate masses, fat or sugar masses or the like, have different characteristics, especially as far as the flow characteristics in the liquid state depending on the temperature of the masses are concerned. Thus, using some of theses masses, it is sufficient to vary the angle of inclination in which the run-off plate is mounted in the apparatus and/or to use gravity forces to circulate the excess of coating material on the run-off plate. Especially when using thixotrop masses or masses having a low fat content it is not possible to use gravity forces only to circulate excess masses in the region of an inlined mounted run-off plate. A driven unit in form of the scraping belt mentioned above is necessary but having the mentioned disadvantages.
In the above described apparatuses it often is desired to use thixotrop masses or masses having a low fat content as coating material while at the same time using a protection warming circuit to avoid a so-called xe2x80x9cbuild-upxe2x80x9d of such coating materials on the run-off plate during use in a production line to coat articles like chocolate bars, pralines, waffles, ice cream, sugar products, fine baked goods, snacks or the like.
Briefly described, the present invention provides an apparatus for coating articles. The apparatus may be especially used with thixotrop masses or masses having a low fat content as coating material. The apparatus may also be applied with a warming water jacket as a warming medium to prevent subcooling of the coating material.
The apparatus for coating articles includes an endless conveyer belt for transporting the articles to be coated through the apparatus. The liquid coating material circulates in a circulation direction in surplus through the apparatus and freely flows in a downward direction to coat the articles. A tub includes a run-off plate being located below the endless conveyer belt and being designed and arranged to collect the surplus coating material. A driven unit is designed and arranged to assist the circulation of the surplus coating material being located on the run-off plate, and it includes a plurality of doctor blades having lower edges. The doctor blades are arranged above the run-off plate, and they extend in a transverse direction with respect to the surface of the run-off plate. The lower edges of the doctor blades are designed and arranged to be moved parallel and at a distance with respect to the surface of the run-off plate to contact the surplus coating material being located on the run-off plate, and to push it in the circulation direction.
The invention is based on the concept that it is not necessary, but often even disadvantageous, even when using thixotrop masses or masses having a low fat content as coating material, to drive the unit in form of the scraping belt continuously. The direct contact of the struts with the surface of the run-off plate guarantees that all of the excess material being on the surface of the run-off plate participates in the circulation immediately. But disadvantageously, the boundary layer of the coating material on the surface of the run-off plate is destroyed continuously. A substantial heat flux and heat transfer is effected from the protection heating of the double jacketed housing and as well from the sliding action of the struts on the surface of the run-off plate into the coating material. This is a great disadvantage for the tempering of the coating material. Furthermore, the incorporation and mixing of air into the coating material varies the characteristics of the coating material in an undesired manner.
According to the present invention it is sufficient to let the unit having the doctor blades penetrate like a shovel or blade intermittently from time to time into the surface region of the coating material on the run-off plate in order to push the coating material stepwise or batchwise. The stepwise pushing of the coating material can be effected by a continuous or an intermediate drive of the unit assisting the recirculation of the surplus coating material on the run-off plate. This stepwise pushing to make the coating material to move even shows the effect that the coating material on the run-off plate remains in motion when the doctor blades have emerged from the coating material. The apparatus includes the novel unit for assisting the recirculation of the surplus coating material on the run-off plate causes a careful stepwise penetration into the coating material. An incorporation of substantial amounts of air is prevented. The heat flux is practically avoided.
It is of general importance that the doctor blades operate without contact to the surface of the run-off plate i.e. not to use a scraping belt as in the prior art. This brings the advantage that according the distance an insulating layer of coating material is build up between the lower edges of the doctor blades and the surface of the run-off plate, the insulating layer hindering the undesired heat flux into the coating material on the surface of the run-off plate. This makes it possible to control the protection heating of the run-off plate with a higher temperature in order to improve the running characteristics of the coating material in the boundary layer on the run-off plate without negatively influencing the tempering conditions of the coating material. The distance of the lower edges of the doctor blades from the surface of the run-off plate can be chosen or adapted to the special masses used and is in the amount of about 2 to 7 mm, especially 5 mm. Such a distance is sufficiently large to let the insulating layer grow. On the other hand, this distance is small enough not to prevent a motion within the insulating layer. Thus, advantageously the entire coating material participates on the circulation.
The doctor blades of the driven unit are moved in a motion path or a path of movement having a rectangular shape. The motion path is composed of a forward stroke, a upward stroke, a backward stroke and a downward stroke. This can be effected by a pneumatic or a mechanical drive being operated continuously or intermittently. Even the cycle of the several strokes can be interrupted by time periods.
The doctor blades of the driven unit should have a width larger than the usual thickness of the surplus coating material on the run-off plate to avoid incorporation of air into the coating material. On the other hand, the entire material contacted by the doctor blades is pushed forwardly on the run-off plate. The doctor blades of the driven unit during the backward stroke completely get free from any contact to the coating material. This is the case with a stepwise drive and a continuous drive also.
A pneumatic drive an be provided for the driven unit assisting the recirculation of the surplus coating material on said run-off plate. The pneumatic drive can have two piston/cylinder units adapted to each other and controlled to effect said motion path having rectangular shape. But it is possible also to provide a mechanic drive for the driven unit assisting the recirculation of the surplus coating material on the run-off plate, the mechanical drive having cam discs.
The driven unit assisting the recirculation of the surplus coating material on the run-off plate can be allocated to a part of the run-off plate or to the run-off plate as a whole.
The doctor blades can be located at an angle of about 30xc2x0 with respect to the plane of the surface of the runt-off plate. The inclination of the arrangement of the doctor blades is directed away from the run-off plate. Depending on the arrangement of the doctor blades with respect to the surface of the run-off plate during penetration of the doctor blades into the coating material on the run-off plate a slight backward motion of the coating material on the run-off plate can happen due to the inclined arranging of the doctor blades and the adaptation of the movements of the drive of f.e. the two piston/cylinder units. This backward motion is not useless but acts as a loosening action of the coating material at its place on the run-off plate. In this manner the coating material is started to move, especially when using an intermediate drive for the unit. It is evident, that this slight backward motion of the coating material is reversed by the following forward stroke which is longer.
Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and the detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention, as defined by the claims.